At level 100, the "magic" Leftovers number is any number that is evenly divisible by 16 + 1.
What is the "magic" Leftovers number at level 50?
I will give you some sixteenth/ leftover numbers: 144 (Hitmontop, that should be the lowest of the high HP in the metagame), 160, 176, 192 (for most base 100 mons).
These numbers should be avoided in normal circumstances, but since there are less passive hazards in Lv.50 battles, it is enough just to have that much HP - or one more, just to be safe.
If you want to know: To create 51-subs you need 204 HP. At Lv 100 those base 100 Mons can't exceed that number, so they have to stick on 404 (where they can't sub as often as one withShade 405).
At Lv 50 though they manage to have 205 , so a SubCM one might hit that number.
Nevertheless, Seismic toss and Night are extremely rare down there.
Next question...
At level 100, 4 EVs = 1 stat point
At level 50, χ EVs = 1 stat point
What is χ equal to?
Lv 0-19: 40
Lv 20-29: 20
Lv 30-39: 13,3
Lv 40-49: 10
Lv 50-59: 8
Lv 60-69: 6,7
Lv 70-79: 5,75
Lv 90-99: 4,4
Lv 100: 4
At Lv 50, you need 8 EV for one stat point, at Little Cup 40.